Application of cast aluminum for engine structures has been increasing in recent years. These new applications include engine components for high power density and heavy duty service that were traditionally cast from gray iron. Individual aluminum alloy castings produced within a single production run can vary substantially in mechanical and physical properties. For example, tensile properties may vary between regions or locations in the same casting due to differences in local rates of solidification. Variations may also occur between castings due to slight changes within the acceptable limits for adding of the constituents to form the alloy and the latitudes of time and temperature of heat treatment and processing.
Historically, the tests conducted for determining the physical properties of a casting tended to destroy or weaken the casting. More recently, a testing method has been developed that is based on a relationship that correlates a microstructural parameter of a dendritic alloy sample to ductility. The method includes counting substantially all of the metal dendrite arms of the primary metal phase within a surface area of a selected location and correlating the number of metal dendrite arms per unit area to the ductility of the location. The number of dendrite arms is correlated to the ductility of the dendritic alloy by means of an equation: ##EQU1##
where
EL=total average elongation (ductility) in percent, PA1 N=number of cells of the primary metal of the alloy counted per unit area, and PA1 A, B, C, D=empirical constants. PA1 EL is the total average elongation (ductility of casting in percent), PA1 N is the number of cells of the primary metal of the casting per unit area, PA1 C.sub.1 (NO.sup.0.5) is the solidification rate, PA1 ##EQU3## PA1 is the solidification rate (SR), PA1 ##EQU4## PA1 is the SR and eutectic modification (EM) interaction; AR is the aspect ratio of the eutectic particles, PA1 ##EQU5## PA1 is the EM from alloying and solution heat treatment, PA1 C.sub.4 (P.sup.0.5) is the porosity, percent coverage, ductility reduction, PA1 C.sub.5 is a coefficient characteristic of the chemistry of the alloy, and PA1 c, k, and b are empirical constants for the alloy and PA1 C.sub.1, C.sub.2, C.sub.3, and C.sub.5 are coefficients from statistical multiple regression of the alloy.
Further effort has refined the ductility equation to account for porosity of the sample. The method includes selecting a surface area of the casting for determining ductility; determining the number of metal cells of the primary metal within the surface area of the casting; measuring the aspect ratio of the eutectic particles and the porosity within the surface area of the casting; and determining ductility of the casting by relating the number of cells of primary metal per unit area with the measured aspect ratio of the eutectic particles and the measured porosity according to the equation: ##EQU2##
where
While progress has been made, designing components for high power density, heavy duty automotive applications reveals a lack of detailed information on the metallurgy of solidification of the aluminum alloys sufficient to predict mechanical and physical properties. It is desirable to predict physical and mechanical properties before a casting is made.